/*
 * Copyright (C) 2012 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.hash;

import com.google.common.base.Supplier;

import java.util.concurrent.atomic.AtomicLong;

/**
 * Source of {@link LongAddable} objects that deals with GWT, Unsafe, and all that.
 *
 * @author Louis Wasserman
 */
@ElementTypesAreNonnullByDefault
final class LongAddables
{
    private static final Supplier<LongAddable> SUPPLIER;

    static
    {
        Supplier<LongAddable> supplier;
        try
        {
            new LongAdder(); // trigger static initialization of the LongAdder class, which may fail
            supplier =
                    new Supplier<LongAddable>()
                    {
                        @Override
                        public LongAddable get()
                        {
                            return new LongAdder();
                        }
                    };
        }
        catch (Throwable t)
        { // we really want to catch *everything*
            supplier =
                    new Supplier<LongAddable>()
                    {
                        @Override
                        public LongAddable get()
                        {
                            return new PureJavaLongAddable();
                        }
                    };
        }
        SUPPLIER = supplier;
    }

    public static LongAddable create()
    {
        return SUPPLIER.get();
    }

    private static final class PureJavaLongAddable extends AtomicLong implements LongAddable
    {
        @Override
        public void increment()
        {
            getAndIncrement();
        }

        @Override
        public void add(long x)
        {
            getAndAdd(x);
        }

        @Override
        public long sum()
        {
            return get();
        }
    }
}
